Inorganic electroluminescent devices are known in the art. The device generally comprises a thin film of phosphor disposed between two electrodes, one of which is transparent. The phosphor generally comprises zinc selenide doped with manganese, europium or terbium. Upon application of a current, the phosphor emits light. Anthracene crystals are also known in the art as an electroluminescent material. However, devices made from these materials require high voltages for operation and have low efficiency.
Organic electroluminescent devices (structure and composition) are also known in the art as disclosed in U.S. Pat. No. 4,356,429 (col. 2-4) and 5,408,109 (col. 5-7), the disclosures of which are incorporated herein by reference for all purposes. There is a desire in the industry to develop an organic polymeric electroluminescent material which efficiently emits deep blue light without excimer formation. Excimer formation causes an undesired color shift in the emission and generally also a loss of efficiency.
Substituted polyfluorenes are known in the art as electroluminescent materials. Although substituted polyfluorenes emit predominantly blue light, they are deficient because they form excimers with red-shifted emission and often form poor films, and can be intractable polymers.
Anthracene dispersed in a polymeric binder is also known in the art as an electroluminescent material. However, these materials are deficient because, as a guest/host system, they aggregate and crystallize, lowering luminous efficiency. These materials also require high voltages to operate. Main chain anthracene homopolymer is intractable and unsuitable. Further, Yamamoto et al. report the inability to make main chain copolymers of anthracene in Macromolecules, Vol. 25, 1992, page 1214.
It is therefore an object of the present invention to provide an improved electroluminescent device.
Other objects and advantages will become apparent from the following disclosure.